Origin of Life Theories & Characteristics of Living Things

Vocabulary flashcards covering major theories on life’s origin and the defining characteristics of living organisms.

Life (biological definition)

Ability to reproduce, grow, and generate energy through chemical reactions using external materials.

Theory of Special Creation

Religious idea that all organisms were created simultaneously in their present, fully-formed state with no evolution or adaptation.

Extraterrestrial Origin (Cosmozoic / Panspermia)

Hypothesis by Richter and Arrhenius that life reached Earth as resistant spores from another planet.

Theory of Spontaneous Generation (Abiogenesis)

Ancient belief that living organisms arise directly from non-living matter.

Van Helmont

Proponent of spontaneous generation who claimed mice could form from a dirty shirt and wheat in 3 weeks.

Francesco Redi

Disproved spontaneous generation for maggots by covering meat jars; no maggots appeared in sealed containers.

Lazzaro Spallanzani

Showed that boiled broth in sealed flasks stayed free of microbes, challenging spontaneous generation.

Louis Pasteur

Used swan-neck flasks to prove microbes come from airborne dust, finally refuting spontaneous generation.

Biochemical Evolution (Physico-Chemical Theory)

Modern concept by A.I. Oparin & J.B.S. Haldane that life arose from chemical evolution under early Earth conditions, not possible today.

Chemogeny

Stage of chemical evolution where simple organic molecules first formed on early Earth.

Biogeny

Stage where the first cell-like structures emerged, bringing life from non-living matter.

Cognogeny

Diversification phase in which single-celled organisms evolved into varied multicellular forms.

Precambrian

Eon comprising Hadean, Archean, and Proterozoic; spans Earth’s earliest history before complex life.

Hadean

Earliest Precambrian era with no atmospheric oxygen.

Archean

Precambrian era when cyanobacteria began producing oxygen via photosynthesis.

Proterozoic

Later Precambrian era marked by rising oxygen and more complex single-celled life.

Organization (life characteristic)

Living beings are highly ordered structures composed of cells that form tissues, organs, and systems.

Metabolism

All chemical reactions and energy transformations sustaining life, enabling growth, repair, and activity.

Catabolism

Metabolic pathway that breaks down organic matter, releasing energy.

Anabolism

Metabolic pathway that uses energy to build cellular components.

Growth

Irreversible increase in size of an organism or its parts.

Development

Progression from a simpler to a more advanced or mature form.

Movement & Locomotion

Ability of an organism or its parts to change position; includes plant tropisms and nastic movements.

Tropism

Directional growth response toward or away from an external stimulus.

Nastic Movement

Non-directional plant response where movement is independent of stimulus direction.

Irritability

Capacity of an organism to perceive and respond to stimuli.

Reproduction

Process by which organisms generate offspring, ensuring species continuity.

Sexual Reproduction

Reproductive mode involving gametes, resulting in genetic variation.

Asexual Reproduction

Reproduction without gametes, producing genetically identical offspring.

Adaptation

Inherited traits that improve an organism’s survival or reproductive success in a specific environment.

Chemical Composition of Life

Living matter mainly consists of carbon, hydrogen, oxygen, and nitrogen in specific arrangements.

Homeostasis

Ability to maintain stable internal conditions despite external environmental changes.